In the construction of radial ply tires, various tire components are assembled together sequentially around a tire building drum. The assembled components are shaped around the drum into the desired toroidal form of the tire. The shaped tire is then cured for added strength and durability.
The various tire components typically include a fluid impervious inner liner onto which is applied one or more corded carcass ply layers. The carcass ply layers terminate in a pair of tire beads which provide the means to mount the tire to a rim. Adjacent the one or more carcass ply layers are sidewall portions and a tread portion. The tread portion may include one or more circumferential reinforcing belts.
When the tire is in service, it is susceptible to damage due to stresses and road hazards. The portion of the tire near the tire beads resists damage because it is generally thicker than the sidewalls and receives added support from the tire rim. The tread portion is also thicker than the sidewalls and may benefit from the added strength provided by the reinforcing belts. The sidewalls of the tire are therefore more susceptible to road hazards due to their relative thinness as compared to the tire beads and tread portion. This is especially the case near the upper sidewall, which is the sidewall portion near the edge of the tread. Moreover, the directionality of the cord in the carcass plies near the upper sidewalls permits greater flexing and bulging, making this area of the tire more susceptible to in-service damage. Hence, the upper sidewall portions of the tire often contribute significantly to the overall failure rate of a radial tire.
Manners of increasing the strength of a tire sidewall are known. For example, U.S. Pat. No. 4,573,511 to Kabe, et al. provides a support layer for a tire sidewall which is applied to the structure of the carcass cord layer. The support layer overlaps the belt reinforcing layers under the tread at one end, thereby functioning as a load bearing member for tire inflation stresses. The other end of the support layer is attached to a bead portion within close proximity of the tire bead, the distance between this end of the support layer and the bead of the tire being less than three-tenths of the cross sectional height of the tire. The support layer is designed to reduce the tire weight while maintaining the high speed durability and load capacity of the tire.
U.S. Pat. No. 4,287,929 to Huinink also discloses reinforcements for tire sidewalls. A reinforcing insert consisting of a polyamide such as nylon is placed externally of the tire carcass on each side of the tire. The upper edge of each of the reinforcing inserts is sandwiched between the tire carcass and the tread belts, enabling the inserts to absorb inflation stresses, and the lower edges of the reinforcing inserts are partially wrapped around the tire bead cores.
Securing a sidewall support layer at one end under the tread, however, presents manufacturing problems, especially when modeling the tire into its final shape. The upper sidewall area of the tire near the ends of the belt reinforcing layers, due to its excessive curvature, is a difficult portion of the tire to form. Any overlap of layered material, such as the belt reinforcing layers and the sidewall support layers, within the tire near this area may cause formation defects such as trapped air pockets or a rippled outer appearance of the tire. Defects in this portion of the tire present a problem due to the significant stresses to which this portion of the tire is subjected during service. Thus, defects in this area of the tire pose a particular risk of tire failure.
A similar problem presents itself if the lower ends of the sidewall reinforcements are wrapped around the beads of the tire. Because the tire carcass is typically turned up around the tire bead, the overlapped carcass plies and the reinforcement layers may cause formation defects near this portion of the tire, such as trapped air pockets or a rippled outer appearance of the tire.
It is an object of the present invention, then, to provide a protective barrier for a tire sidewall which is located between the tire carcass and the sidewall and which provides protection against upper sidewall punctures. It is a further object of the present invention to provide a method of forming a tire having a protective sidewall barrier which substantially reduces or eliminates formation defects in the tire.